Distribution of HABs throughout the World

Several decades ago relatively few countries appeared to be affected by HABs, but now most coastal countries are threatened, in many cases over large geographic areas and by more than one harmful or toxic species. Many countries are faced with a bewildering array of toxic or harmful species and impacts, as well as disturbing trends of increasing bloom incidence, larger areas affected, more fisheries resources impacted, and higher economic losses. The causes behind this expansion are debated, with possible explanations ranging from natural mechanisms of species dispersal to a host of human-related phenomena such as pollution, climatic shifts, increased numbers of observers, and transport of algal species via ship ballast water.

Whatever the mechanisms, coastal regions throughout the world are now subject to an unprecedented variety and frequency of HAB events. The global expansion of HAB phenomena is in part a reflection of our ability to better define the boundaries of the problem - the nature and extent of toxic or harmful species and their impacts. However, the fact that part of the expansion is attributable to increased scientific awareness and detection capabilities should not temper our concern. The involvement of human activities in the HAB expansion suggests that policy decisions leading to bloom mitigation are needed at several levels, but sound scientific evidence is needed to justify these actions. Studies of human influences are ongoing in many areas, but are in their early stages of investigation.